A transmission system of this kind is disclosed, for example, in the patent DE 197 33 546 C1. In that publication it is proposed to construct at least one gear module as an angular gear, which can be combined with a plurality of drive modules. The angular gear module is specified as a crown gear, the crown wheel of which is adapted to engage each of the output pinions of a drive motor. However, if it is desired to encompass very large ranges of transmission ratios, with the known transmission modules several gear housings must be provided, because crown gears customarily allow transmission ratios to vary merely within a range of about 1-6. The additional transmission stages (with spur wheels) proposed in that publication also allow only limited variation within a single housing.
Another modular transmission system is known from the patent EP 0 557 961 B1. As input stage an axially offset angular gear is proposed, specifically a bevel gear, and as the subsequent additional transmission stages cylindrical gears are shown. The problem area associated with this system corresponds to that described above. In particular, it is also impossible here to accommodate a very large range of transmission ratios.
One object of the present invention is to provide a modular transmission system that in a simple manner permits a large range of transmission ratios.
This and other objections and advantages are achieved by the modular transmission system according to the invention, in which one and the same housing accommodates either a spiroplan transmission stage or a crown-gear transmission stage, while employing the same offset and the same bore. The particular advantage here is the large range of transmission ratios that results, because a spiroplan transmission stage and a crown-gear transmission stage enable transmission ratios to vary widely. The ratios for a crown-gear stage are about 1-6, while those for a spiroplan stage are 6-200. Overall, then, with this modular system a transmission-ratio range of 1-200 can be covered with only one transmission stage in a single housing.
Regarding the spiroplan gearing, it should be noted that here the term is meant to denote gearings belonging to the category of angular gears. These are employed to transmit power between intersecting or crossing shafts. From a kinematic viewpoint, this is a spiral bevel gearing that resembles a worm-gear mechanism, except that unlike a worm gear, in this case a cylindrical worm meshes with a planar crown wheel as mating gear and not with a globoid worm wheel. The offset provided here is achieved by a curved longitudinal configuration of the teeth of the wheel. A spiroplan gearing is described, for example, in the applicant's patent DE 43 09 559.
In contrast, the crown-gear arrangement (according to Nieman Winter, Vol. III, Section 24.1.3) amounts kinematically to a pair of bevel gears in which the profile displacements change along the width of the teeth, in such a way that a cylindrical pinion and a planar crown wheel as mating wheel are produced. In the case of a straight-toothed pinion and axial offset the longitudinal tooth-flank shape of the wheel is a straight line, whereas with an oblique-toothed pinion it is curved.
In particular, therefore, the proposed solution of the problem cited above is a modular transmission system with least one structural element, encased in a housing, that comprises a plurality of gearings with different transmission ratios, in each of which there is a first transmission stage that comprises an angular gear with axial offset incorporating an input drive pinion that meshes with a planar crown wheel having teeth that project parallel to the axis. In this system the axial offset is the same for all the transmission stages in a given structural element, and there are provided at least one first pinion with a first such planar crown wheel having a crown-gear tooth configuration and a second pinion with a second such planar crown wheel having a spiroplan tooth configuration.
Preferably the housing also includes a second transmission stage that is rotationally connected to the input drive stage and that comprises at least two cylinder gears. This enables the range of transmission ratios to be expanded.
In a first preferred embodiment the planar crown wheel in the first transmission stage is connected by way of a common bearing shaft to a pinion in the second transmission stage, so that the angular gear constitutes an input drive stage. Especially advantageous in this regard is the fact that when running rapidly, this transmission stage makes less noise than would be achievable with cylinder or bevel gears. Given that an angular stage is always more expensive than a cylinder-gear stage of the same size, a saving in expense is also obtained, because the site of action of the lower torque can be of smaller dimensions. A tooth-bearing adjustment like that for worm-gear or bevel-gear mechanisms is thus not needed here.
In another embodiment of the invention an output wheel of the second transmission stage is connected to the input drive pinion of the first transmission stage, by way of a common bearing shaft, so that the angular gear forms an output-drive stage. The advantage of this arrangement lies in the fact that the cylinder gears already available in standard kits (in particular those supplied by the applicant) can be used, so that their transmission-ratio variability can be exploited economically. Nevertheless, by this means only two or three different transmission ratios of the output angular-gear stage (in particular spiroplan stage) are needed to provide a sufficient range of ratios. Here, again, the construction of the transmission system is simple and requires no tooth-bearing adjustment such as is required for worm- or conical-gear mechanisms. The result is an especially shock-absorbing and low-noise operation. Another important point in this regard is that the axial offset of the pinion makes room for the cylinder-gear transmission stage, so that the system as a whole can be of particularly flat construction.
In particular in the embodiment in which the angular gear constitutes the output drive stage, it is advantageous for the housing to contain apparatus for flange-mounting a motor, such that the input-drive cylinder gear of the second stage is attached to an output shaft of the motor. This construction is especially economical and compact.
Altogether, the axial offset preferably amounts to between 2/10 and 4/10 of the diameter of the planar crown wheel.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.